1. Field of the Invention
The invention relates to polymeric viscosity index (V.I.) improvers-dispersant additives for petroleum oils, particularly lubricating oils whereby oil solutions, particularly oil concentrates, of said additives are characterized by minimal viscosity change over an extended period of time. These additives comprise a copolymer of ethylene with one or more C.sub.3 to C.sub.28 alpha-olefins, preferably propylene, which have been grafted with acid moieties, e.g. maleic anhydride, preferably using a free radical initiator in a solvent such as a lubricating oil, and then reacted with a carboxylic acid component and a polyamine having two or more primary amine groups, or preformed salts, amides, imides, etc. formed by the reaction of said carboxylic acid component with said polyamine, and subsequently treated or reacted with a viscosity stabilizing effective amount of at least one C.sub.12 to about C.sub.18 hydrocarbyl substituted dicarboxylic acid anhydride, preferably C.sub.12 to C.sub.18 hydrocarbyl substituted succinic anhydride. The invention also relates to process for preparing the preceding products and their use in oil compositions.
2. Description of the Prior Art
U.S. Pat. No. 4,517,104, incorporated herein by reference, discloses polymeric viscosity index (V.I.) improver-dispersant additives for petroleum oils, particularly lubricating oils, comprising a copolymer of ethylene with one or more C.sub.3 to C.sub.28 alpha-olefins, preferably propylene, which have been grafted with acid moieties, e.g. maleic anhydride, preferably using a free radical initiator in a solvent, preferably lubricating oil, and then reacted with a mixture of a carboxylic acid component, preferably an alkyl succinic anhydride, and a polyamine having two or more primary amine groups. Or the grafted polymer may be reacted with said acid component prereacted with said polyamine to form salts, amides, imides, etc. and then reacted with said grafted olefin polymer. These reactions can permit the incorporation of varnish inhibition and dispersancy into the ethylene copolymer while inhibiting cross-linking or gelling.
U.S. Pat. No. 4,632,769, also incorporated herein by reference, discloses oil soluble viscosity improving ethylene copolymers such as copolymers of ethylene and propylene, reacted or grafted with ethylenically unsaturated carboxylic acid moieties, preferably maleic anhydride moieties, and then reacted with polyamines having two or more primary amine groups and a C.sub.22 to C.sub.28 olefin carboxylic acid component, preferably alkylene polyamine and alkenyl succinic anhydride, respectively. These reactions can permit the incorporation of varnish inhibition and dispersancy into the ethylene copolymer while inhibiting cross-linking or gelling.
While these additives are very useful oil compositions, particularly concentrates, thereof tend to exhibit increased viscosity over an extended period of time. Therefore, there exist a need for additives whose oil solutions, particularly oil concentrates, exhibit less viscosity change over an extended period of time.
The source of the viscosity increase over an extended period of time of oil solutions of these additives appears to be, at least in part, due to the chain extension of the polymer. Several solutions to this problem are described in the prior art. One solution is to use the polyamines and then to react the remaining unreacted primary amino groups with acid anhydrides of either C.sub.1 -C.sub.30 monocarboxylic acid, preferably acetic anhydride, or unsubstituted or C.sub.1 to C.sub.8 hydrocarbyl substituted dicarboxylic acid anhydrides of U.S. Pat. No. 4,137,185; or the sulfonic acids of U.S. Pat. No. 4,144,181. These materials act as polyamine group end-capping or inactivating agents to inhibit or limit chain extension. That is to say, the reaction product of the graft copolymer of the ethylenically unsaturated dicarboxylic acid material and polyamine is post-treated with these acid materials to inhibit chain extension and viscosity increase of the imide grafted ethylene copolymer.
While the end-capping or amine inactivating agents disclosed in U.S. Pat. Nos. 4,137,185 and 4,144,181 are generally quite useful, their utilization results in some problems under certain conditions. Thus, for example, reacting a monocarboxylic acid anhydride, e.g., acetic anhydride, with the polyamine yields an acid byproduct, e.g., acetic acid. This acid is deleterious to engine operation, causing corrosion, and generally needs to be removed from the oil solution of the V.I. improver-dispersant. Furthermore, the use of the unsubstituted or lower hydrocarbyl substituted dicarboxylic acid anhydrides of U.S. Pat. No. 4,137,185 generally does not remedy, and may sometimes even contribute to, the formation of haze in oil solutions of the imide grafted ethylene copolymer. This is due to the fact that when using free radical initiators with mineral oil as the grafting medium a proportion of the oil molecules in turn become grafted with the ethylenically unsaturated moiety, e.g., maleic anhydride, and upon subsequent reaction with the amine these grafted oil particles tend to become insoluble and to form haze. Upon the addition of the hydrocarbyl substituted dicarboxylic acid anhydrides to this oil solution to inactivate the unreacted primary amine groups of the imide grafted ethylene copolymer, a certain proportion of the anhydride reacts with the free amine groups of the grafted oil particles. Since the prior art anhydrides are either unsubstituted or lower hydrocarbyl substituted they do not facilitate the solubilization of these insoluble grafted oil particles. However, since the dicarboxylic acid anhydrides of the instant invention are substituted with a C.sub.12 to C.sub.18 hydrocarbyl group they tend to facilitate the solubilization of the insoluble grafted oil particles, thereby decreasing haze.
The use of the sulfonic acids of U.S. Pat. No. 4,144,181 may also result in the formation of undesirable acid by-products, e.g., hydrogen sulfide.
Furthermore, these prior art end-capping or primary amine inactivating agents do not, in all instances, provide a sufficient degree of viscosity stability for some applications to oil solutions of the additives of this invention.
It has been found that improved viscosity stability over an extended period of time of oil solutions, particularly oil concentrates, of the imide grafted ethylene copolymers of this invention can be achieved while remedying the problems of acid by-product formation and hazing accompanying the utilization of the prior art amine group end-capping or inactivating agents by utilizing a C.sub.12 to C.sub.18 hydrocarbyl substituted dicarboxylic acid anhydride as the polyamine end-capping or chain extension terminating agent.